1. Field of the Invention
The present invention relates to a spin transistor and a method of manufacturing the same.
2. Related Background Art
Attention has recently been focused on studies about spin electronics. Spin transistors, which are transistors utilizing spins of electrons, have been expected to bring about new technological innovations. The spin transistors can be employed as storage devices having new structures (see Japanese Patent Application Laid-Open No, 2004-111904 and International Publication Pamphlet WO2004/079827) and multifunctional logic circuits (see International Publication Pamphlet WO2004/086625). They are made by magnetic material processes and thus may also be used as control devices for magnetic devices.
In particular, FIG. 11 of Japanese Patent Application Laid-Open No. 2004-111904, FIG. 4 of U.S. Pat. No. 6,873,545B2, and FIG. 4 of U.S. Pat. No. 5,654,566 disclose spin transistors in which a nonmagnetic semiconductor layer is interposed between two ferromagnetic metals constituting source and drain electrodes, respectively, while a gate electrode layer is provided on the semiconductor layer with a gate insulating layer interposed therebetween or a gate electrode is provided in Schottky contact with the semiconductor layer.
In such conventional spin transistors, the source electrode injects spin-polarized electrons into the semiconductor layer. Namely, the source electrode has both functions of a typical electrode and a spin-polarized electron injection layer. The polarizing direction of electrons injected into the semiconductor layer depends on the magnetization direction of the source electrode, while the spin polarization ratio of electrons injected into the semiconductor layer depends on the spin polarization ratio of the source electrode acting as the spin-polarized electron injection layer.
The electrons injected into the drain through a channel of the semiconductor layer are scattered depending on the direction of their polarization. In other words, the electrons injected into the semiconductor channel from the source electrode are subjected to spin-dependent scattering on the drain electrode side. Namely, the drain electrode has both functions of a typical electrode and a spin filter layer for preferentially receiving electrodes polarized in a specific direction. Therefore, the resistance between the source and drain electrodes becomes smaller and greater when the source and drain electrodes are magnetized in directions parallel and antiparallel, respectively, to each other.